Two important trends in modern information management and communications technology are the increasingly higher circuit densities used in electronic systems and the increased use of lightwaves for transmitting information. For long distance transmission of information, optical fibers are increasingly replacing conductive cable and radio transmission systems. Higher device densities are manifested as higher circuit densities on both microelectronic chips and printed wiring boards (PWBs).
Electronics systems are typically organized by mounting various system components on PWBs and interconnecting the PWBs with a circuit transmission element known as a backplane. The backplane may include various socket elements for receiving printed wiring boards; the PWBs may be supported by troughs or shelves in parallel arrays such that they contact a socket when inserted in the shelves. As the circuit density of the printed wiring boards increases, it becomes increasingly difficult to provide the needed backplane interconnections because, as interconnection transmission lines become thinner, their impedances increase. Moreover, the distance over which information must be transmitted by backplane conductors is normally fairly long compared to the distances transmitted on printed wiring boards. These factors may reduce the speed at which the circuits can be operated, which may defeat a principal advantage of higher circuit densities.
In addressing these problems, it has been suggested that more of the electronic system be interconnected by optical fibers or other optical waveguides. For example, the paper, "Glass Waveguides on Silicon for Optical Hybrid Packaging," C. H. Henry, G. E. Blonder and R. F. Kasaranov, Journal of Lightwave Technology, Vol. 7, No. 10, October 1989, pp. 1530-1539, describes a method for using photolithography to define glass optical waveguides in a manner similar to the photolithographic definition of printed circuits. Such "printed circuit" optical waveguides always have a much greater loss than optical fibers, and it is recognized that they are practical only for transmitting information over a short distance. Moreover, significant optical losses invariably result from abrupt changes of direction of optical waveguides so that it is difficult to use optical waveguides to transmit light from one substrate to another.
Accordingly, there has been a long-felt need for apparatus that is easy to use and that can efficiently transmit large quantities of information between circuit component substrates such as printed wiring boards.